The invention relates to (5-alkylureido-1,3,4-thiadiazol-2-yl-thio) acetic acid esters. (5-alkylureido-1,3,4-thiadiazol-2-yl-thio)-carboxylic acid esters have already been proposed in general form for use as herbicidal agents (West-German Pat. No. 1,817,949) without, however, identifying specific active agents. Subsequent tests have shown that for instance [5-(1,3-dimethylureido)-1,3,4-thiadiazol-2-ylthio]-acetic acid ethylester (b.p. 113.degree. C), [5-(1,3,3-trimethylureido)-1,3,4-thiadiazol-2-ylthio]-acetic acid ethylester (b.p. 95.degree. C) and [5-(3-methylureido)-1,3,4-thiadiazol-2-ylthio]-acetic acid isopropylester (b.p. 143.degree. C) has no herbicidal activity.